Over a hundred thousand years ago, Neanderthals used tar to bind objects together, yet scientists have struggled to understand how these ancient humans, with their limited knowledge and resources, were able to produce this sticky substance. A new experiment reveals the likely technique used by Neanderthals, and how they converted tree bark into an ancient form of glue.

Neanderthals were manufacturing their own adhesives as far back as 200,000 years ago, which is kind of mind blowing when you think about it. We typically think of fire, stone tools, and language as the “killer apps” of early human development, but the ability to glue stuff together was as much of a transformative technology as any of these.

Tar produced from the experiment seen dripping from a flint flake. (Image: Paul Kozowyk)

New research published in Scientific Reports reveals the startling ingenuity and intellectual capacities of Neanderthals, and the likely method used to cook up this ancient adhesive.

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Based on the archaeological evidence, we know that Neanderthals were manufacturing tar during the Middle Pleistocene Era. The oldest traces of this practice date back to a site in Italy during a time when only Neanderthals were present in Europe. Similar tar lumps and adhesive residues have also been found in Germany, the oldest of which dates back some 120,000 years ago. The Neanderthals used tar for hafting—the practice of attaching bones or stone to a wooden handle to create tools or weapons. It was a force multiplier in engineering, allowing these ancient humans to think outside the box and build completely new sets of tools.

What makes the presence of tar at this early stage in history such a mystery, however, is that Neanderthals had figured out a way to make the useful goo thousands of years before the invention of ceramics, which by the time of the ancient Mesopotamians was being used to produce tar in vast quantities. For years, archaeologists have suspected that Neanderthals performed dry distillation of birch bark to synthesize tar, but the exact method remained a mystery—particularly owing to the absence of durable containers that could be used to cook the stuff up from base materials. Attempts by scientists to replicate the suspected Neanderthal process produced tar in miniscule amounts and far short of what would be required for hafting.

To finally figure out how the Neanderthals did it, a research team led by Paul Kozowyk from Leiden University carried out a set of experiments. Tar is derived from the dry distillation of organic materials, typically birch bark or pine wood, so Kozowyk’s team sought to reproduce tar with these substances and the cooking methods likely at the disposal of the Neanderthals. It’s very likely that the Neanderthals stumbled upon the idea while sitting around the campfire.

Tar collected in a birch bark “container.” (Image: Paul Kozowyk)

“A tightly rolled piece of birch bark simply left in a fire and removed when partially burned, once opened, will sometimes contain small traces of tar inside the roll along the burned edge,” explained the authors in the study. “Not enough to haft a tool, but enough to recognize a sticky substance.”

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With this in mind, the researchers applied three different methods, ranging from simple to complex, while recording the amount of fuel, materials, temperatures, and tar yield for each technique. Their results were compared to known archaeological relics to see if they were on the right (or wrong) track. By the end of the experiments, the researchers found that it was entirely possible to create tar in the required quantities using even the simplest method, which required minimal temperature control, an ash mound, and birch bark.

The maximum amount of tar obtained from a single experimental attempt was 15,7 grams—far more than any tar remains from the Middle Paleolithic Era. (Image: Paul Kozowyk)

“A simple bark roll in hot ashes can produce enough tar to haft a small tool, and repeating this process several times (simultaneously) can produce the quantities known from the archaeological record,” write the researchers. “Our experiments allowed us to develop a tentative framework on how the dry distillation of birch bark may have evolved, beginning with the recognition of small traces of birch bark tar in partially burned bark rolls.” They added: “Our results indicate that it is possible to obtain useful amounts of tar by combining materials and technology already in use by Neandertals.”

Indeed, by repeating even the simplest process, the researchers were able to obtain 15.9 grams of useable tar in a single experiment, which is far more than any tar remains found in Middle Paleolithic sites. What’s more, temperature control doesn’t need to be as precise as previously thought, and a durable container, such as a ceramic container, is not required. That said, the process did require a certain amount of acumen; for this process to come about, Neanderthals needed to recognize certain material properties, such as the degree of adhesiveness and viscosity. We’ll never be certain this is exactly what Neanderthals were doing, but it’s a possibility with important implications for early humans in general.

“What this paper reinforces is that all of the humans that were around 50,000 to 150,000 years ago roughly, were culturally similar and equally capable of these levels of imagination, invention and technology,” explained Washington University anthropologist Erik Trinkaus, who wasn’t involved in the study, in an interview with Gizmodo. “Anthropologists have been confusing anatomy and behavior, making the inference that archaic anatomy equals archaic behavior, and ‘modern’ behavior [is equivalent to] modern human anatomy. What is emerging from the human fossil and Paleolithic archeological records across the Eurasia and Africa is that, at any one slice in time during this period, they were all doing—and capable of doing—basically the same things, whatever they looked like.”

“What this paper reinforces is that all of the humans that were around 50,000 to 150,000 years ago roughly, were culturally similar and equally capable of these levels of imagination, invention and technology,”

Sabrina Sholts, an anthropologist at the Smithsonian Institute’s National Museum of Natural History, says this study is a nice example of how experimental archaeology can be used to supplement the material record and address questions about past hominid behavior.

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“I think it’s certainly worthwhile to test methods of tar production that could have been used by Neanderthals and early modern humans, if only to challenge our assumptions about the kind of technologies—and ideas—within their reach,” she told Gizmodo.